You are correct but are missing the forest for the trees as they say.

The original mutation is random, benefiting (or at least not harming) is selected for. So without the random mutation there isn't anything being selected for.

For example, say we need to change gene 1 from A to C for the fever to last 1 hour longer (this is very simplified of course) but throughout history no one has changed gene 1 to C then there will be no longer fever to select for.

We can't see evolution as something that moves creatures along with intent. Nothing is guaranteed since you must first have a random mutation to progress.

There also isn't a reason to think the body would evolve a way to stay in fever after vital load drops. Remember, evolution is random and if this never randomly occurred we wouldn't evolve it.

This is the worst kind of amateur take.

Humans have generally had a few days to weeks of fat reserve plus some extra weeks with muscle. The calorie cost of raising your temp 4°F is low. Plus, we have, since becoming human and probably long before, lived in groups (often familial) that help each other.

80% is the threshold for Apple to recommend a battery. That’s when messages like this generally start appearing.

Emphasis mine.

Yeah, sure, I'm Steve Jobs, so I know what I'm talking about.

You said the message and the battery degradation percentage are connected.

You're wrong. These shouldn't occur at 80%. Apple recommends replacement at 80%, that doesn't mean the battery is unable to provide the necessary amperage at 80%.

You are doubling down because you don't want to be wrong, it's okay to be wrong.

What does this message say?

I'm pretty sure it says that performance was affected. Thus, you are arguing with yourself. You are saying Apple gives these messages when the phones performance is affected by decreased battery capacity at 80%, yet that battery capacity isn't affected until less than 80%.